Quantum teleportation achieved over ten miles of free space

Scientists have recently had success teleporting information between photons …

Quantum teleportation has achieved a new milestone or, should we say, a new ten-milestone: scientists have recently had success teleporting information between photons over a free space distance of nearly ten miles, an unprecedented length. The researchers who have accomplished this feat note that this brings us closer to communicating information without needing a traditional signal, and that the ten miles they have reached could span the distance between the surface of the earth and space.

As we've explained before, "quantum teleportation" is quite different from how many people imagine teleportation to work. Rather than picking one thing up and placing it somewhere else, quantum teleportation involves entangling two things, like photons or ions, so their states are dependent on one another and each can be affected by the measurement of the other's state.

When one of the items is sent a distance away, entanglement ensures that changing the state of one causes the other to change as well, allowing the teleportation of quantum information, if not matter. However, the distance particles can be from each other has been limited so far to a number of meters.

Teleportation over distances of a few hundred meters has previously only been accomplished with the photons traveling in fiber channels to help preserve their state. In this particular experiment, researchers maximally entangled two photons using both spatial and polarization modes and sent the one with higher energy through a ten-mile-long free space channel. They found that the distant photon was still able to respond to changes in state of the photon they held onto even at this unprecedented distance.

However, the long-distance teleportation of a photon is only a small step towards developing applications for the procedure. While photons are good at transmitting information, they are not as good as ions at allowing manipulation, an advancement we'd need for encryption. Researchers were also able to maintain the fidelity of the long-distance teleportation at 89 percent— decent enough for information, but still dangerous for the whole-body human teleportation that we're all looking forward to.

'When one of the items is sent a distance away, entanglement ensures that changing the state of one causes the other to change as well, allowing the teleportation of information, if not matter. However, the distance particles can be from each other has been limited so far to a number of meters.'

Doesn't this happen at greater than the speed of light?

I didn't think information could be transmitted using EPR, due to causality?

No information is transmitted. The end state of the two photons is correlated but random. I'm disappointed that such a basic misunderstanding made its way into an article here. I'll ignore the last sentence as the second half of it was presumably a joke.

Whole-body teleportation? Who cares? Exactly HOW fast could this transfer information? If I've understood correctly, the transfer is instantaneous. That means no more relying on silly things like fiber optics that only move stuff at the speed of light (or so).

I don't know if it allows for the information to be "transmitted" between the two particles faster than the speed of light, however even if it does, I don't think that there's any causality violation happening.

Each of the two entangled particles must have existed together very close to each other at one point in time, they are then taken apart from each other - this must happen at less than the speed of light, so each particle is within the light cone of the other.

Does this violate causality? I don't know! Maybe I've been reading too many books by Charles Stross where this exact thing is a plot device - instantaneous communication via entangled particles, however each causal channel has a finite number of bits, due to a finite number of already entangled particles that it contains...

Reading the first couple of comments, it's interesting to note that even if the "transmit information" phrasing in the article was an attempt to dumb things down for a wider audience, it's causing nothing but confusion. This perhaps demonstrates the intelligence of your audience and I would encourage you folks not to take after Wired but stick to your intelligent articles, intelligent audience roots.

Reading the first couple of comments, it's interesting to note that even if the "transmit information" phrasing in the article was an attempt to dumb things down for a wider audience, it's causing nothing but confusion. This perhaps demonstrates the intelligence of your audience and I would encourage you folks not to take after Wired but stick to your intelligent articles, intelligent audience roots.

Ignorance <> lack of intelligence.

I agree that the phrasing was misleading, but how would you have phrased it differently and still appealed to as wide an audience as possible?

Or: explain why you think science articles should only try to inform already-knowlegeable people, instead of also informing and educating laypeople.

Reading the first couple of comments, it's interesting to note that even if the "transmit information" phrasing in the article was an attempt to dumb things down for a wider audience, it's causing nothing but confusion. This perhaps demonstrates the intelligence of your audience and I would encourage you folks not to take after Wired but stick to your intelligent articles, intelligent audience roots.

Ignorance <> lack of intelligence.

I agree that the phrasing was misleading, but how would you have phrased it differently and still appealed to as wide an audience as possible?

Or: explain why you think science articles should only try to inform already-knowlegeable people, instead of also informing and educating laypeople.

I would prefer no article over an article that deliberately misinforms people.

Reading the first couple of comments, it's interesting to note that even if the "transmit information" phrasing in the article was an attempt to dumb things down for a wider audience, it's causing nothing but confusion. This perhaps demonstrates the intelligence of your audience and I would encourage you folks not to take after Wired but stick to your intelligent articles, intelligent audience roots.

Massive douchebag.

I would encourage you to jump off a bridge, how's that for transmitting some information?

You are the one who clearly is a little brain dead, or perhaps so socially inept that you are mistaking ignorance or an optimistic attitude (which is what many have, when Science isn't their first language - Or best friend, in your case Professor Douche).

I think Ars does a great job in making subjects I personally would steer very clear of as usually I visit the site primarily to browse casually - Very approachable.

The problem that I have with it, and I assume this is shared by others, is that transmission of information faster than the speed of light violates causality according to special relativity. That's why the thought experiment that preceded these real experiments is known as the "EPR paradox". There are a number of ways to resolve the paradox, some of which make more sense than others (http://en.wikipedia.org/wiki/EPR_parado ... experiment)

So basically, it would be fine to say what happened at a higher level and then link to a more in-depth source, but it is misleading to simplify it in terms of immediate transmission of information.

Is the issue just that we didn't explicitly say "quantum information" in a story that's exclusively about quantum mechanics? Because it's possible to teleport the state of a qubit, which is what that sentence is referring to, but i have the sense that the unease with the phrasing goes beyond that.

Also, APS physics, which i'd think has some sense of what it's talking about, says this: "Quantum Teleportation: Taking advantage of the so-called spooky action at a distance inherent in quantum entanglement, physicists have been able to transmit quantum information from one system to another across macroscopic distances."

I'm adding "quantum" to the sentence, but, given the context, i didn't think it was essential here, and the purpose of the sentence was to contrast this technique with expectations of Star Trek style teleportation.

I think that a lot of the reaction stems from a natural defensiveness that people develop because they are so used to seeing science misrepresented on sites like slashdot. I, at least, tend to overreact because it depresses me to read all of the bizarre conclusions that people come to after reading and misunderstanding short articles on complicated topics.

Heavens no. Don't let people dream of the possibilities within the capacity of their knowledge. Elitism cry foul! Right or incorrect, it gets people interested and possibly encourages some to find out even more.

I'm an idiot, so... I really don't understand the difference between that and this: taking two balls, one white, and one black, and placing them randomly into two identical boxes. I give one box to my friend who drives 3000 km across the country, at which point I open my box and *instantly* know the information contained in his.

I guess what I mean is it seems everything needs to be setup in the same place then separated, so I don't understand the magic of knowing what is over there when it had to be overhere in the first place --how does this mutuate into sending a continuous stream of 0's and 1's?

I think it's a fair assumption that most of the readers wishes to learn more about quantum teleportation but don't really understand it. As one of those poor souls, let me state:I don't get it.

We are teleporting 'quantum' information, and this actually happens instantaneously?But quantum infromation isn't 'real' information so we're not violating causality?If it's not 'real' information, then what the hell is it good for and how could we ever do anything useful with it?(Such as encryption or matter teleportation as alluded to in the article.)

Davis- I think the transmission of the 1s and 0s could be achieved by utilizing parallelism with the quantum bits. For example, if you entangled 8 pairs and then moved them apart, you could manipulate the bits in one place and see that manipulation in the other. I guess it isn't really "sending" the information as we typically understand it, but rather instantaneous mirroring of state manipulation that can be interpreted in binary fashion.That seems possible with what's been achieved here. I'm no dummy but I'm certainly not well versed in quantum entanglement so if someone who is can pick my idea apart and point out any errors I would appreciate it.This is wild stuff!

Regarding "information" vs. "quantum information": I think most of us non-science types assume information is an external bit (i.e. the letter "a") as opposed to the quantum state information which is an internal/integral part of the interaction (I think-IANAS). So for those of us skipping in, information transmission has a different connotation, and from that we go in a different direction (after all, most of us don't really know quantum theory/mechanics/etc.). While Ars Science stuff is great (I love it, though a large portion is out of my realm, so I'm not sure I always understand it) it does help to include more specificity so us laypersons can anchor to it more easily. The trick is in getting the right info included so we have the right anchors- it's a fine line, and you guys often do it very well.

Yes, nkinnan is being a real dick (seriously man- you offered nothing up to clarify the point, just bitched about what was there, and then insulted the rest of the audience. Classy. BTW-I know many things you don't-but hoarding and sticking up my nose wouldn't even occur to me- explaining and clarifying would) but there is a kernel of useful info there.

Either way- it is an interesting result, though the entanglement process stills blows my mind when I think too much about it (since I have no training beyond physics 101).

I guess the potential problem is here: "When one of the items is sent a distance away, entanglement ensures that changing the state of one causes the other to change as well, allowing the teleportation of quantum information, if not matter."

I would write "measuring" instead of "changing" to be more correct, but don't have a serious problem with it. Many people who don't understand physics think that they understand causality limits, so perhaps change "causes" to a safer word, too.

Everyone, two classical bits, describing the random measurement result, must be sent from one side to the other before the quantum bit can be recovered. Thus causality is not violated. (Actually experimentalists like to perform "postselected" teleportation, which means that they send "0" if the two bits are 00 and allow failure the other 3/4 of the time. Yes, this is lame.)

Before I ask this question, I feel like I should state that I have no physics background beyond the 2 introductory (algebra based) courses I was required to take in college.

Once perfected, couldn't we use something like this on satellites that we send into space? Then again, from the comments thus far, it looks like changing the bits in one place and seeing results in the other instantaneously would violate causality?

Honestly, I don't even know if my questions make sense as stated - this is how lacking my knowledge is in this area.

I think quantum assisted communication methods allow for a more secure communication. I think this just allows quantum communication to go wireless (still requires a wireless decoder signal). This means that satellites can be made more secure. Anyway, I found the entire article here:http://www.nature.com/nphoton/journal/v ... 010.87.pdf

I too winced when I read that information was being communicated 10 miles instantaneously. These kinds of statements will definitely mislead others into thinking Orson Scott Card was right all along and one day a new life form will develop on the invisible strings connecting these entangled pairs...

The biggest let down on my life so far was understanding how little we have ventured into space. It was a misunderstanding I had as a 3-10 year old watching movies and cartoons... I am still lost without moon hotels and space fighters. Don't give me instantaneous communication and then take it away again... I just can't take another let down!

Ok, I remember reading that once entangled, these particles can communicate over space and time. So if this is the case and using the Hawking theory of time travel. We could accelerate one particle to near the speed of light and have it travel to the future while it's counterpart is still here at our time. Allowing the scientists of the future to send us messages and vice versa. This could exponentially advance technology and of course cause the universe to explode.

Is it possible to measure whether a stream of photons are in a superposition? Let's say I aim the stream at a filter that lets vertically polarized photons through and reflects horizontally polarized ones. Then I use mirrors to get the two possible paths to line up before they strike a photon detector. If the photon has a definite polarity it takes either one path or the other, if it's a superposition it takes both, then lines up with itself again causing interference patterns at the detector. Shouldn't this setup be able to tell me whether I'm receiving a stream of particles with a definite polarity or not? And shouldn't that tell me whether I'm receiving a stream of particles that have had their entangled partner's state measured? And couldn't we use that to communicate a bit of information?

I'm sure it's not that simple, but where does the protection of causality jump in and invalidate that experiment?

Ok, I remember reading that once entangled, these particles can communicate over space and time. So if this is the case and using the Hawking theory of time travel. We could accelerate one particle to near the speed of light and have it travel to the future while it's counterpart is still here at our time. Allowing the scientists of the future to send us messages and vice versa. This could exponentially advance technology and of course cause the universe to explode.

Just saying.

Yeah that's a plot device in the Alistair Reynolds 'Revelation Space' series of novels. A device called Exordium used by a a faction of humanity to communicate with future scientists.